Probing the interaction mechanism of heterostructured VO_xN_y nanoparticles supported in nitrogen-doped reduced graphene oxide aerogel as an efficient polysulfi'de electrocatalyst for stable sulfur cathodes

摘要

Reversible redox of sulfur to lithium sulfide through a series of lithium polysulfides (LiPS) still pose a key challenge to appreciate high-performance sulfur cathodes mainly because of shuttling phenomenon and sluggish kinetics. Herein, a simple novel synthetic approach has been presented to realize porous vanadium nitride oxide (VOxNy) nanoparticles spatially decorated within nitrogen doped reduced graphene aerogel (VONNG) via concurrent in-situ nitridation and carbonization processes. Nitrogen-doped reduced graphene aerogel enhances the physical retention and polar interaction of LiPS and contributes toward the overall conductivity of the matrix. Whereas, vanadium nitride oxide has exhibited a redox potential window intermediate to its oxides' counterparts around which LiPS can form polythionate complexes to enhance the kinetics and LiPS retention by exploiting the V-N and V-O interfaces at cathode. The interaction mechanism has been probed through in-operando Raman spectroscopy, XPS and electroanalytical methods. The assembled cells from VONNG/S cathodes exhibit the initial discharge capacity of 1400 mAh g(-1) at 0.05 C, 1250 mAh g(-1) at 0.1 C and maintained reversible capacity about 700 mA h g(-1) at 0.2 C after 200 cycles. The loss in capacity is less than 0.05% per cycle for 850 cycles with Coulombic efficiency close to 99% even at 5C.